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Proton beam therapy for cancer causes fewer side effects than conventional radiotherapy, research suggests.

The study, published in The Lancet Oncology, suggested the therapy is also as effective as other treatments.

It pointed to similar survival rates and a lower impact on heart and lungs.

In 2014 the therapy was at the centre of a controversy over NHS care for children when the parents of Ashya King took him out of hospital in Hampshire to obtain the treatment abroad.

Their actions led to a police operation to find them.

Ashya, then aged five, is now cancer free, his family said last year.

The study, which was led by Dr Torunn Yock from the Massachusetts General Hospital in the US, looked at 59 patients, aged between three and 21, between 2003 and 2009.

'Alternative therapy'

All the patients had the most common kind of malignant brain tumour in children, known as medulloblastoma.

After five years, their survival rate was similar to that of patients treated with conventional X-ray radiotherapy, but there were fewer side effects to the heart and lungs, the study found.

The paper said: "Proton radiotherapy resulted in acceptable toxicity and had similar survival outcomes to those noted with conventional radiotherapy, suggesting that the use of the treatment may be an alternative to photon-based treatments."

What is proton beam therapy?

It uses charged particles instead of X-rays to deliver radiotherapy for cancer patients.

The treatment allows high-energy protons to be targeted directly at a tumour, reducing the dose to surrounding tissues and organs.

In general, it gives fewer side effects compared with high-energy X-ray treatments.

It can be used to treat spinal cord tumours, sarcomas near the spine or brain, prostate cancer, lung cancer, liver cancer and some children's cancers.

Independent expert Prof Gillies McKenna, who is the head of the department of oncology at the University of Oxford, said the research suggested that the "side effects are indeed dramatically reduced" with proton beam therapy.

"There were no side effects seen in the heart and lungs and gastrointestinal tract, which are almost always seen with X-rays, and no secondary cancers were seen at a time when we would have expected to see them in X-ray treated patients," he added.

Proton beam therapy is currently only available in the UK to treat eye cancers, but patients with other forms of cancer can apply for NHS funding for the therapy abroad.

However, the Department of Health has said that from April 2018 the treatment will be offered to up to 1,500 cancer patients at hospitals in London and Manchester, following investment worth £250m.

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Two years ago a dispute about the use of the treatment prompted Brett and Naghemeh King, of Southsea, Hampshire, to remove Ashya from a hospital in Southampton against his doctors' advice.

The parents had wanted their son to undergo proton beam therapy in Prague, which had not been recommended by his care team in Southampton.

Their actions sparked an international police manhunt, and the couple were later arrested and held in a prison in Madrid.

They were eventually released and Ashya's therapy took place, with the NHS later agreeing to pay for it.

A spokesman for University Hospital Southampton NHS Foundation Trust, said that medulloblastoma was not currently on the list of tumours approved for this treatment on the NHS.

"However, we welcome any update to the existing clinical evidence on cancer treatments and will follow any expansion of the current national criteria," a spokesman added.

Key events for Ashya's treatment

• Ashya had surgery for a medulloblastoma brain tumour at Southampton General Hospital in July 2014
• His parents, Brett and Naghemeh, removed him from the hospital on 28 August and sparked a manhunt when they travelled to Spain
• They were arrested but later released and Ashya was flown to Prague, Czech Republic, for proton beam treatment
• He had six weeks of proton beam therapy, which cost between £60,000 and £65,000, according to the treatment centre, and which was paid for by the NHS
• Ashya returned to hospital in Spain
• In March 2015, Brett King announced his son was free of cancer